This invention relates to an image pickup element for a photoelectric converter used for a facsimile and, more particularly, to a thin film image pickup element or two-dimensional thin film image pickup element used for facsimile.
A charge coupled device (CCD), a metal oxide semiconductor (MOS) or other type of thin film sensor has heretofore been used as a solid image pickup element. There exists no thin film sensor which is stereoscopically constructed with a photoelectric converting unit and switching unit. Recently, thin film sensors have been used in which an amorphous semiconductor is superposed as a photoelectric converting element on the upper surface of a MOSFET with a monocrystalline silicon wafer. However, this conventional solid image pickup element cannot be fabricated to have a size larger than the monocrystalline silicon wafer, nor can it be formed in a multilayer at the switching unit due to the properties of the monocrystalline silicon wafer.
Since the conventional one-dimensional thin film sensor is so constructed that its sensor, switching transistor and wiring pattern are all formed on the same plane, it is disadvantageous in that it requires a substrate much larger than the area of the sensor and cannot be formed in a two-dimensional shape due to structural reasons.
Further, a CCD or the like has heretofore been employed as a two-dimensional image pickup device. The two-dimensional image pickup device is fabricated by superimposing an amorphous semiconductor on the upper surface of a MOSFET in a monocrystalline silicon wafer. Since this image pickup device, however, necessitates a reducing optical system, it is disadvantageous in that its structure becomes complicated and it is therefore difficult to fabricate in a large area, thus making it difficult to read a two-dimensional original document.
There also exists a type of conventional one-dimensional image pickup device in which a driver is fabricated by a silicon IC chip and another type in which a thin film transistor, which will be hereinafter referred to as a "TFT", is formed laterally. However, the first type in which a drive is fabricated by a silicon IC chip requires a large number of bonding portions between the wiring pattern and the IC chips, and is therefore impractical. The other type in which a thin film transistor is laterally formed is constructed so that its optical converting element and a switching element are formed on the same plane, and therefore has difficulty in reading a two-dimensional original document.